A. Field of the Invention
This invention pertains to electroluminescent devices, and more particularly, to devices incorporating at least one light emitting layer made of a polymer material combined with a thin film solar cell providing an electrical current.
B. Background of the Invention
Electroluminescent (EL) devices have become popular as lighting sources for watches, clocks, radios, and the like. Early EL devices were capable of generating light only at a single wavelength, and were very rigid and fragile. More recently, electroluminescent materials have been discovered which are flexible so that they can be shaped into various geometric configurations. Typically, such electroluminescent devices include one or more layers of a semiconductive conjugated polymer (generally referred to as light emitting polymer or LEP) placed between two contact layers. The contact layers are used to inject charge carriers into the polymer layer. These charge carriers then combine within the polymer layer into charge carrier pairs which decay, generating radiation in the visible wavelengths. Devices of this type can be incorporated into various apparatus for generating light. U.S. Pat. No. 5,828,117 discloses, for example, a luminescent device with two light emissive layers adapted to radiate light of two colors.
It is an objective of the present invention to provide a composite device which includes an EL source and a coextensive solar cell.
A further objective is to provide a composite device of the type described above in which, at least in one configuration, electrodes are shared between the two components thereby reducing its complexity and thickness.
Other objectives and advantages of the invention shall become apparent from the following description.
Briefly, a device constructed in accordance with this invention includes at least two spaced, layered semiconductor components: a light emitting component adapted to selectively generate light in the presence of an electrical field, and a generating component capable of generating electricity. Several display elements may be formed in the light emitting component which cooperate to selectively generate images. The light emitting component may include for instance an LEP or other EL materials.
The generating component is made of a thin film semiconductor material adapted to generate an electric current in response to light. The thin film semiconductor material may comprise an active layer made, for example, of amorphous silicon adapted to generate positive and negative charges when light impinges thereon.
Each component is provided with electrodes. The electrodes for the light emitting component are used to apply the required electrical field, and the electrodes of the generating component are provided to collect the positive and negative charges within the thin film, which charges result in a current flow. In an alternate embodiment of the invention, an electrode is shared between the two components. The electrodes may be provided in the form of layers of a conductive material.
The light emitting component may be formed of a plurality of discrete light emitting elements disposed, for instance, in a two-dimensional array. Semiconductor switches may also be provided to selectively activate these discrete light emitting elements. A non-conductive transparent material is provided between the discrete light emitting elements to complete the light emitting component. This material allows external light to propagate through the display component and to impinge on the generating component.